Telephone-transmitter



E. C. WENTE.

TELEPHONE TRANSMITTER.

I APPLICATION FILED DEC. 20,1916. I n 1,3335744.; Patented Mar. 16, 1920.

`,lr/'7J l 4obo 4000 sooo f77. 4. 26 J6 III! www@ H O 2/ J2 2.5 26 v l I [I 22 IM www,

y" 'Y wim/.M

UNITED sTATEs PATENT oEEroE.

EDWARD C. 'WENTE, OF NEW HAVEN, CONNECTICUT, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

I TELEPHONE-TRANSMITTER.

To all whom t may concern:

Be it known that I, EDWARD C. WENTE, a citizen of the United States, residing at 162 York St., New Haven, in the county of New Haven and State of Connecticut, have invented certain new and useful Improvements in Telephone-Transmitters, of which the following is a full, clear, concise, and exact description.

This invention has reference to improvements in .telephone transmitters for the reproduction, recording, analyzing and measuring of sound Waves.

More particularly it relates to telephone transmitters lof the condenser type, its object being to produce a transmitter that gives practically a uniform transmission over a far greater range of frequency than has 4heretofore been obtained. y

' It has been found that diaphragme, such as are usedin telephones, phonographs and other acoustic apparatus, have a more or less marked natural period for one or more frequencies and if acted upon by impulses of these frequencies will respond much more than for materially `different periodicities. The natural period depends in general on the mass and the elasticity of the diaphragm, decreasing -with increase of mass, and increasing with increase of elasticity. In the usual telephone diaphragm, the

,lowest natural period is in the neighborhood of 1000 cycles per second which is well within the range of those frequencies used lin speech. Because of this natural periodicity and the resulting inequality of response to impulses-of different frequencies, a telephone diaphragm will distort the speech waves which are impressed onit when the resonance point falls "within that range which is of importance in speech. If, however, the elasticity of the transmitter is increased suiiiciently, this resonance pointwill be removed outside the speech range and there will be practically equal response to all impressed frequencies of the same intensity and consequently there will be little or no distortion of the impulsesv impressed on the diaphragm. This maximum response at the resonance point can also be considerably decreased in value by,.increas ing the damping factor of the vibrating system. The damping factor in 'general der Specification of Letters latent.

Patented Mar. 16, 1920.

Application filed December 20, 1916. Serial No. 187,978.

which would be represented by a line parallel to the axis of frequency, indicating theren by an equal response to all frequencies.

This invention has for its purpose primarily to make improvements in the quality of speech as transmitted by previous telephonic or phonographic apparatus and accomplishes this purpose by increasing the elasticity and the damping factor of the vibrating system.

For the accomplishment of the objects above set forth, this invention embodies a transmitter of sound waves consistingof a sheet of stretched material and a stationary member in close face to face relation with each other. The close adjustment of the two members to each other greatly increases the elasticity of the diaphragm and its damping coeilicient in a manner hereinafter described, so thatthe natural period peak is removed beyond the upper limit of the frequency range of importance to speech and is reduced to a minimum.

For the better understanding of this invention, it is described in connection with a condenser transmitter althoughthe lscope of the invention is not limitedthereto, but

it may be applied to any type of a vibration' instrument without departing in any wise from the spirit of this invention.

The novel features of this invention are particularly pointed out in the appended claims, for a better understanding of which reference is made to the following. descrip Fig.V 3 illustrates a Vcross sectional View of" a condenser transmitter illustrating one embodiment of this invention.

Fig. 4 represents an application of this invention to the reproduction or recording of sound Waves.

The resonance curve of a stretched diaphragm is somewhat similar in form to that shown in Fig. 1, in which F represents. the frequency of the impulses incident upon the diaphragm, and I represents the degree of response of the diaphragm tothe incident frequencies. Such a diaphragm has a natural period of vibration and transmits vibrations in the neighborhood of that period with far greater intensity than other vibrations. An unstretched telephone diaphragm may have a natural frequency in the neighborhood of one thousand cycles per second but by suitable stretching this natural frequency can be raised to the neighborhood of 4000 cycles asshown in .the figure. Such a diaphragm would be undesirable for the analysisl or accurate reproduction of sound waves because of the great emphasis with which vibrations of a certain pitch would be brought out to the detriment of the other incident frequencies, thereby producing distortion. In this description we shall consider that the upper limit of the frequency range of importance to speech is approximately 8000 cycles per second. v

Fig. 2 gives the resonance curve forthe `,Vibrating system embodied in this invention in which the resonance peak is outside the frequency range important to speech, being in the neighborhood -of F=16000 cycles. Hence there will be practically a uniform responsiveness for-the whole speech range. The change from Fig. 1 to Fig. 2 is brought about' by increasing to a high degree the elasticity and the damping factor of the vibrating system according to the means embodied in this invention and described in connection with a condenser transmitter.

In the condenser transmitter illustrated in,

Fig. 3' of the drawing, the diaphragm 6 and the plate 7 constitute the two plates 'of the condenser part of the transmitter. Sound waves, incident on the diaphragm, cause it to vibrate, thereby causing variations in the effective thickness of the dielectric between the plates and consequently giving rise to -variations in the capacity of the condenser.

The diaphragm 6 is shown clamped near its outer edge by means of the clamping rings 8 and 9. Ring 11 has, in contact with the diaphragm, a Iprojection 12 that serves to stretch the diaphragm when 'suitable compression is exerted between'the clamping rings 8 and 9 and' the ring 11 by means of the bolt 13. The'back electrode or plate 7 is fastened to an insulating disk 14 of suitable insulation material such as amber or glass. This disk rests in a recess 15 of the bushing 16 in such a manner that, when the rim of the bushing machined and polished. For a final adjustment of the gap, it may be found desirable to inserta thin Washer of mica 10, or other suitable material in the recess l5, in which the insulating disk rests.- The diaphragm may be stretched by any of the suitable methods known in the art. 17` is a' locking ring for the insulating disk and thebushing; 18 is a locking ring for the bushing and the stretched ring.

Such an arrangement brings into play the high elastic and frictional forces that are necessary' to increase the frequency Value atwhich the'natural period occurs. When the diaphragm moves in toward the plate, for example, two types of motion take place in the thin film of air between the diaphragm 6 andthe plate 7, namely, a lateral escape toward the periphery ofl the plate and a compression. On account of the extremely narrow passage way between the two elect'rodes, a large frictional force comes into p'lay so that the lateral motion ofl the air is greatly impeded. Being unable to escape, the air undergoes a compression, thereby7 giving additional stiffness' to the system, which is equivalent to increasing the effective elasticity. For example, `:a diaphragm of sheet steel 1.5 inches in diameter, stretched to the lelastic limit, may be made to have a natural frequency'of about 4000 -and, when the vibrations are in air, a damping coefficient of about 1000. If the same stretched.

diaphragm is placed in a vcondenser trans mitter with a plate adjusted to Within adapted to be used as an instrument for reproducing, recording or measuring sound 20 1s a condenser transmitter of thel type vherein described. Connected to one terminal of the condenser is the heated filament 21 of a thermionicV amplifier 22. To the other terminal of the condenser is connected the grid element 28 of the amplifier,

this amplifier being the usual thermionic amplifier of the'faudion type now wellknown in the art. Its output circuit contains the primary transformer winding 25. The secondary winding 26 may be included in a suitable receiving circuit for thc-amplified electric oscillations from the amplifier which are proportional in intensity and magnitude to the signal waves impressed on the transmitter. 28 is a battery or other direct source of current of electromotive circuit of the amplifier 22, which wouldfappear in amplified form in its output circuit 32, Vwhere they would be either passed on to another amplifier for further amplification, or connected to a system containing a suitable'receiving or recording device.

The arrangement of the circuit just described does notvform a part of this invention but is described and claimed in a c0- pending application of Hartley, Serial No. 53,429, filed September 30, 1915. This invention relates solely to the device shown in Fig. .3. Although this device is shown and described as a telephone transmitter it is to be understood that it may serve equally well as a receiver, and although it has been shownA as a condenser transmitter or receiver, it may be used equally well with an electromagnetic receiver or transmitter or a microphonic transmitter by such obvious changes as will occur to any one skilled in the art. In other words the invention consists broadly in adjusting a diaphragm which vis to vibrate in accordance with speech waves, so close to an adjacent face that the inclosed body of air will act to very largely increase the effective elasticity and damping coefficient of the vibrating diaphragm. l f

What is claimed is:

1. A telephone device comprising a vibrating member the normal natural frequency of which is within the range of speech frequencies, and means for increasing the natural frequency of said vibrating member above the range of essential speech frequencies.

Y 2. A device for the transmission of sound composed of two members, saldmembersbemg in face to face relatlon but having their ma- 'jor portions out of contact with each other y and yet so close together as to provide a means for greatly increasing the elasticity of the system. v

3. A device for the transmission of sound provided .with two electrodes, one of' said electrodes constituting a vibrating member l having a natural period of vibration,said

electrodes being in face to face relation' and situated so. -closeltog`ether that the lowest natural frequency of vibration of said device is beyond the frequency range of importance in speech.

4. A telephone transmitter composed of two members, saidmembers being in face to face relation with each other, one of said members constituting a vibrating element having natural frequencies of vibration, the other of said members consisting of a plate separated from said vibrating member by a thin film of a fluid dielectric, said film belng a means for causing the lowest natural frequency of said vibrating member to occur at a frequency |beyond the speech range.`

5. In atelephone transmitter, the combination, of two electrodes, said electrodes having the areas of their facing portions suiiciently extensive to establish an appreciable electrostatic relation between them, one of said electrodes being a sheet of stretched material, said electrodes being in a close face to face relation, thereby greatly increasing the elasticity of said sheet.

6. In a telephone transmitter, the combination of two electrodes, said electrodes having the areas of their facing portions suficiently extensive so as to establish an appreciable electrostatic relation between them, one of said electrodes being a stretched diaphragm, the other being a plate in close proximity to said diaphragm, the two electrodes being so close to each other that the damping of said diaphragm is thereby greatly increased and that the lowest natural vibration frequency of said diaphragm occurs at a frequency beyond the speech range.

7. A`device for the transmission of-sound comprising two members, one of said members being a diaphragm, said members being in such close face to face relation that the movement of the inclosed film of air laterally is appreciably retarded by friction, whereby the elasticity of the diaphragm is greatly increased.

8. A device for the transmission of sound comprising two members, one of said members being a diaphragm, said members being in lose face to face relation with each other, aniii'means comprising a film of air of less than 25 ten thousandths .of an inch in thickness, whereby the elasticity of the diaphragm is greatly increased.

9. A telephone transmitter comprising two members in close face to face relation and having their major portions out of contact with each other a distance less than 25 ten thousandths of an inch.

10. A telephone transmitter comprising two members in close face to face relation, one of said members being a diaphragm, said members having their major portions out of contact with each other a distance less'than 25 ten thousandths of an inch.

11. A telephone transmitter comprising a relation and having. their major portions out of Contact with each other a distance less than ten thousandths of an inch.

12. A telephone transmitter comprising two members in close face to face relation with each other, one of said members being a stretched diaphragm, said members having their major portions out of contact with each other a distance less than 25 ten thousandths 10 of an inch.

13. A telephone transmitter comprising a stretched diaphragm and a rigid plate in close face to face relation with each other, and having their major portions out of contact with each other a distance less than 25 ten thousandths of an inch.`

In Witness whereof, I hereunto subscribe my name this ifteenth day of December, A. D., 1916.

EDWARDC. WENTE. 

